(1) Field of the Invention
The present invention relates to microfilm readers for microfiche films used as information retrieving apparatus.
(2) Description of Related Art
Microfilm readers for microfiche films such as microfilm reader-printers are widely used as apparatus for retrieving information by projecting images recorded on microfiche films onto a screen.
One such microfilm reader comprises a microfiche supporting device (which is hereinafter referred to in the Description of Related Art as a microfiche moving mechanism) for sandwiching the microfiche film in sheet form between an upper glass plate and a lower glass plate and moving the microfiche film longitudinally and transversely, and a projecting optical system for projecting images recorded on the microfiche film onto the screen. As shown in FIG. 1, a principal portion of the projecting optical system includes an exposure lamp 211, a condenser lens 212 and a reflecting mirror 213 arranged below the microfiche moving mechanism having lower glass plate 201 and upper glass plate 202 as main components thereof for sandwiching microfiche film F. The above three optical elements constitute a light-source side of the system for illuminating the microfiche film F. On the side upward of the microfiche moving mechanism, the projecting optical system includes a projecting lens 214 housed in a lens case 214a placed on the upper glass plate 202, and an image turning prism 216 housed in a holder 215 to be coaxial with the projecting lens 214. These optical elements project light which has passed through the microfiche film F onto the screen via a projecting mirror 217.
The microfiche film F is searched for a desired image recorded thereon by moving the lower glass plate 201 and upper glass plate 202 together in X-Y directions instead of moving the the projecting optical system. In this case, the upper glass plate 202 and projecting lens 214 are in contact with each other and, therefore, the lower end of the projecting lens 214 slides on the top surface of the upper glass plate 202. Moreover, since the projecting lens 214 and image turning prism 216 are arranged coaxially to form a unit, the lens case 214a, as a whole, has a considerable weight which results in their being a heavy load on the upper glass plate 202.
Where the microfiche moving mechanism for moving the upper and lower glass plates 202 and 201 is automated with a motor or the like, the movement thereof is faster and more frequent than manual movement. However, this gives rise to the problem that the projecting lens 214 tends to make many scratches on the surface of upper glass plate 202.
If, on the other hand, the upper glass plate 202 were formed of hard glass which is scratch-resistant, it would render the manufacturing process difficult and increase the cost.
A proposal has been made to so arrange the projecting lens 214 that it is out of sliding contact with the upper glass plate 202. However, this proposal is hardly practicable since, with the projecting lens spaced from the upper glass plate, a high degree of planar precision is required of the microfiche moving mechanism because a projecting lens providing a high magnification rate is often used for projecting the images recorded on the microfiche film and such a lens has a small depth of focus.
There are also microfilm readers of the autoloading type which automatically transport the microfiche film to and from a position between the upper and lower glass plates of the microfiche moving mechanism. Accordingly, as disclosed in Japanese Patent Publications 53-47006 and 55-25406, the upper glass plate is lifted in timed relationship with movement of the microfiche moving mechanism to the home position for loading and unloading the film.
The known means of lifting the upper glass plate by utilizing the movement of the microfiche moving mechanism as mentioned above has the following disadvantages:
(1) If an attempt is made to lift the upper glass plate with weak strength, the lifting means must have a very long stroke from the point of view of strength. This results in an increase in the size of the microfiche moving mechanism.
(2) Where this lifting means is used in the autoloading type reader, rollers of the loading device fail satisfactorily to engage and discharge the microfiche film if the film becomes curled during an unloading operation.
(3) Since the microfiche moving mechanism moves during a period following insertion of the microfiche film between the upper and lower glass plates of the microfiche moving mechanism until the upper glass plate is fully lowered, mechanism is required for engaging and holding the film during this time against displacement from a correct position. Such a mechanism lends complexity to the construction.